1. Field of the Invention
This invention relates to a radiation image recording and read-out method and apparatus, wherein a radiation image is stored on a stimulable phosphor sheet, the stimulable phosphor sheet, on which the radiation image has been stored, is exposed to stimulating rays, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to radiation, the emitted light is detected, and the radiation image is thereby read out from the stimulable phosphor sheet and converted into an electric signal. This invention particularly relates to an improvement in an erasing light source.
2. Description of the Related Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then exposed to stimulating rays, such as a laser beam, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then processed and used for the reproduction of the radiation image of the object as a visible image on a recording material. The radiation image recording and reproducing systems described above are referred to as computed radiography (CR).
The applicant proposed built-in types of radiation image recording and read-out apparatuses, comprising: (i) circulation and conveyance means for conveying at least one stimulable phosphor sheet along a circulation path, (ii) an image recording section, which is located in the circulation path and in which a radiation image of an object is stored on the stimulable phosphor sheet, (iii) an image read-out section, which is located in the circulation path and in which the radiation image is readout from the stimulable phosphor sheet, and (iv) an erasing section, which is located in the circulation path and in which energy remaining on the stimulable phosphor sheet after the radiation image has been read out therefrom is released. The built-in types of radiation image recording and read-out apparatuses are disclosed in, for example, U.S. Pat. Nos. 4,543,479 and 4,851,679, and Japanese Unexamined Patent Publication No. 3(1991)-238441. With the proposed built-in types of radiation image recording and read-out apparatuses, the stimulable phosphor sheet is utilized repeatedly and is processed efficiently.
As for the radiation image recording and read-out apparatuses described above, from the point of view of keeping the emitted light detection time short, reducing the size of the apparatus, and keeping the cost low, it has been proposed to utilize a line sensor comprising a charge coupled device (CCD) image sensor, or the like, as photoelectric read-out means. The utilization of the line sensor as the photoelectric read-out means is disclosed in, for example, Japanese Unexamined Patent Publication Nos. 60(1985)-111568, 60(1985)-236354, and 1(1989)-101540.
Basically, the radiation image recording and read-out apparatuses of such types comprise:
i) a read-out unit comprising (a) stimulating ray irradiating means for linearly irradiating stimulating rays onto an area of a stimulable phosphor sheet, on which a radiation image has been stored, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to radiation, and (b) a line sensor, which comprises a plurality of photoelectric conversion devices arrayed along the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays, and
ii) sub-scanning means for moving the stimulable phosphor sheet with respect to the read-out unit and in a direction (a sub-scanning direction), which is approximately normal to a length direction of the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays (a main scanning direction).
In particular, in cases where the radiation image recording and read-out apparatuses are constituted such that the stimulable phosphor sheet is kept stationary, and the read-out unit is moved in the sub-scanning direction, the sizes of the radiation image recording and read-out apparatuses as a whole are capable of being kept small. As an example of the radiation image recording and read-out apparatus having the constitution described above, in order for energy, which remains on the stimulable phosphor sheet after the radiation image has been read out from the stimulable phosphor sheet, to be released, there has heretofore been proposed a radiation image recording and read-out apparatus, wherein an erasing light source is located on the side backward from the read-out unit, and erasing light is irradiated simultaneously to the entire surface of the stimulable phosphor sheet.
However, problems with regard to back scattering are encountered in that, when radiation, such as X-rays, carrying image information of an object is irradiated to the stimulable phosphor sheet, part of the radiation passes through the stimulable phosphor sheet and is scattered within the radiation image recording and read-out apparatus toward the stimulable phosphor sheet. As a result of the back scattering, information different from the image information of the object is stored as an artifact on the stimulable phosphor sheet, and the image quality of the radiation image becomes bad. For example, in cases where the erasing light source is located on the side backward from the read-out unit in the manner described above, the problems often occur in that the radiation having been scattered by the erasing light source impinges upon the stimulable phosphor sheet, and gray level image pattern corresponding to the form of the erasing light source is recorded on the stimulable phosphor sheet.
In order for the problems described above to be eliminated, it may be considered to employ a technique, wherein a lead plate is located on the side of a surface of the stimulable phosphor sheet, which surface is opposite to the surface of the stimulable phosphor sheet exposed to the radiation, and the radiation having passed through the stimulable phosphor sheet is absorbed by the lead plate, such that the radiation having passed through the stimulable phosphor sheet does not any more enter into the radiation image recording and read-out apparatus. However, it is necessary that, after the radiation image has been stored on the stimulable phosphor sheet, the stimulable phosphor sheet and the read-out unit are located in close vicinity to each other, and an operation for reading out the radiation image from the stimulable phosphor sheet is performed in this state. If the lead plate is located on the side of the surface of the stimulable phosphor sheet, which surface is opposite to the surface of the stimulable phosphor sheet exposed to the radiation, it will not always possible for the stimulable phosphor sheet and the read-out unit to be located in close vicinity to each other for the radiation image read-out operation. Therefore, in such cases, the size of the radiation image recording and read-out apparatus cannot be kept small, and the structure of the radiation image recording and read-out apparatus cannot be kept simple.
The primary object of the present invention is to provide a radiation image recording and read-out method, wherein radiation having passed through a stimulable phosphor sheet is prevented from being scattered and again impinging upon the stimulable phosphor sheet, such that a size of an apparatus for carrying out the radiation image recording and read-out method is capable of being kept small, and such that a structure of the apparatus is capable of being kept simple.
Another object of the present invention is to provide an apparatus for carrying out the radiation image recording and read-out method.
The present invention provides a radiation image recording and read-out method, comprising the steps of:
i) supporting a stimulable phosphor sheet at a position for image recording, at which one surface of the stimulable phosphor sheet is exposed to radiation,
ii) exposing the one surface of the stimulable phosphor sheet, which is supported at the position for image recording, to the radiation, a radiation image being thereby stored on the stimulable phosphor sheet,
iii) performing an image read-out operation by irradiating stimulating rays in two-dimensional directions to the stimulable phosphor sheet, on which the radiation image has been stored during its exposure to the radiation, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to the radiation, and photoelectrically detecting the emitted light, an image signal, which represents the radiation image having been stored on the stimulable phosphor sheet, being thereby obtained, and
iv) releasing energy, which remains on the stimulable phosphor sheet after the image signal has been obtained from the stimulable phosphor sheet, by irradiating erasing light to an entire area of the stimulable phosphor sheet with an erasing light source, the erasing light source being located on a side of the other surface of the stimulable phosphor sheet supported at the position for image recording, which other surface is opposite to the one surface of the stimulable phosphor sheet exposed to the radiation,
wherein a filter, which has transmitting properties with respect to the erasing light and has good absorbing properties with respect to the radiation, is located on a side of the erasing light source, which side stands facing the stimulable phosphor sheet.
The irradiation of the stimulating rays in two-dimensional directions to the stimulable phosphor sheet, on which the radiation image has been stored, may be performed in one of various ways. For example, one light beam of the stimulating rays may be deflected in the main scanning direction and the sub-scanning direction, and the stimulable phosphor sheet may be scanned with the light spot of the light beam in two-dimensional directions. Alternatively, one light beam of the stimulating rays may be deflected in the main scanning direction alone and may be moved with respect to the stimulable phosphor sheet in the sub-scanning direction. As another alternative, the stimulating rays may be irradiated linearly to an area on the stimulable phosphor sheet along the main scanning direction, the linear stimulating rays may be moved in the sub-scanning direction, and the stimulable phosphor sheet may thereby be scanned with the stimulating rays in two-dimensional directions. As a further alternative, the stimulating rays may be irradiated simultaneously to the entire area of the stimulable phosphor sheet.
In order for the erasing light to be irradiated to the entire area of the stimulable phosphor sheet, the erasing light may be irradiated simultaneously to the entire area of the stimulable phosphor sheet. Alternatively, the erasing light source maybe moved with respect to the stimulable phosphor sheet, and the erasing light may thereby be irradiated to the entire area of the stimulable phosphor sheet.
In the radiation image recording and read-out method in accordance with the present invention, the filter should preferably be a filter, which transmits only light constituted of light components having wavelengths longer than wavelengths of an ultraviolet region. Also, the filter should preferably be constituted of a material selected from the group consisting of a plastic material, which contains a heavy metal (such as Pb, Bi, or W), and a glass, which contains a heavy metal (such as Pb, Bi, or W).
Further, in the radiation image recording and read-out method in accordance with the present invention, the stimulable phosphor sheet may be kept stationary at the position for image recording, and the image read-out operation (i.e., the irradiation of the stimulating rays to the stimulable phosphor sheet and the detection of the light emitted by the stimulable phosphor sheet) may thereby be performed. Alternatively, after the radiation image has been recorded on the stimulable phosphor sheet, the stimulable phosphor sheet, on which the radiation image has been stored, may be conveyed by conveyance means to an image read-out section, and the image read-out operation may be performed in the image read-out section. In particular, the radiation image recording and read-out method in accordance with the present invention should preferably be modified such that the stimulable phosphor sheet is kept stationary at the position for image recording, and
the image read-out operation is performed with image read-out means, which is located between the stimulable phosphor sheet and the erasing light source.
In such cases, the radiation image recording and read-out method in accordance with the present invention should preferably be modified such that the image read-out means comprises:
a) a read-out unit for irradiating the stimulating rays to the stimulable phosphor sheet in a one-dimensional direction along a main scanning direction and detecting the light, which is emitted by the stimulable phosphor sheet when the stimulating rays are irradiated to the stimulable phosphor sheet in the one-dimensional direction, and
b) unit moving means for moving the read-out unit in a sub-scanning direction.
The sub-scanning direction is the direction intersecting with the main scanning direction. In cases where the read-out unit irradiates the stimulating rays to the stimulable phosphor sheet in the one-dimensional direction along the main scanning direction and is moved in the sub-scanning direction, the stimulating rays are irradiated to the stimulable phosphor sheet in two-dimensional directions. Ordinarily, the sub-scanning direction is normal to the main scanning direction.
The read-out unit should preferably comprise a linear stimulating ray source, which linearly irradiates the stimulating rays to an area of the stimulable phosphor sheet, and
a line sensor, which is located along the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays and photoelectrically detects the light emitted by the stimulable phosphor sheet when the stimulating rays are irradiated to the stimulable phosphor sheet.
The present invention also provides an apparatus for carrying out the radiation image recording and read-out method in accordance with the present invention. Specifically, the present invention also provides a radiation image recording and read-out apparatus, comprising:
i) an image recording section for supporting a stimulable phosphor sheet at a position for image recording, at which one surface of the stimulable phosphor sheet is exposed to radiation,
ii) image read-out means for performing an image read-out operation by irradiating stimulating rays in two-dimensional directions to the stimulable phosphor sheet, on which a radiation image has been stored during its exposure to the radiation in the image recording section, the stimulating rays causing the stimulable phosphor sheet to emit light in proportion to an amount of energy stored thereon during its exposure to the radiation, and photoelectrically detecting the emitted light, an image signal, which represents the radiation image having been stored on the stimulable phosphor sheet, being thereby obtained, and
iii) an erasing light source located on a side of the other surface of the stimulable phosphor sheet supported at the position for image recording, which other surface is opposite to the one surface of the stimulable phosphor sheet exposed to the radiation, the erasing light source releasing energy, which remains on the stimulable phosphor sheet after the image signal has been obtained from the stimulable phosphor sheet, by irradiating erasing light to an entire area of the stimulable phosphor sheet,
wherein a filter, which has transmitting properties with respect to the erasing light and has good absorbing properties with respect to the radiation, is located on a side of the erasing light source, which side stands facing the stimulable phosphor sheet.
In the radiation image recording and read-out apparatus in accordance with the present invention, the filter should preferably be a filter, which transmits only light constituted of light components having wavelengths longer than wavelengths of an ultraviolet region. Also, the filter should preferably be constituted of a material selected from the group consisting of a plastic material, which contains a heavy metal (such as Pb, Bi, or W), and a glass, which contains a heavy metal (such as Pb, Bi, or W).
Further, in the radiation image recording and read-out apparatus in accordance with the present invention, the stimulable phosphor sheet may be kept stationary at the position for image recording, and the image read-out operation (i.e., the irradiation of the stimulating rays to the stimulable phosphor sheet and the detection of the light emitted by the stimulable phosphor sheet) may thereby be performed. Alternatively, after the radiation image has been recorded on the stimulable phosphor sheet, the stimulable phosphor sheet, on which the radiation image has been stored, may be conveyed by conveyance means to an image read-out section, and the image read-out operation may be performed in the image read-out section. In particular, the radiation image recording and read-out apparatus in accordance with the present invention should preferably be modified such that the stimulable phosphor sheet is kept stationary at the position for image recording, and
the image read-out means is located between the stimulable phosphor sheet and the erasing light source.
In such cases, the radiation image recording and read-out apparatus in accordance with the present invention should preferably be modified such that the image read-out means comprises:
a) a read-out unit for irradiating the stimulating rays to the stimulable phosphor sheet in a one-dimensional direction along a main scanning direction and detecting the light, which is emitted by the stimulable phosphor sheet when the stimulating rays are irradiated to the stimulable phosphor sheet in the one-dimensional direction, and
b) unit moving means for moving the read-out unit in a sub-scanning direction.
The read-out unit should preferably comprise a linear stimulating ray source, which linearly irradiates the stimulating rays to an area of the stimulable phosphor sheet, and
a line sensor, which is located along the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays and photoelectrically detects the light emitted by the stimulable phosphor sheet when the stimulating rays are irradiated to the stimulable phosphor sheet.
With the radiation image recording and read-out method and apparatus in accordance with the present invention, the erasing light source for releasing energy, which remains on the stimulable phosphor sheet after the image signal has been obtained from the stimulable phosphor sheet, is located on the side of the other surface of the stimulable phosphor sheet supported at the position for image recording, which other surface is opposite to the one surface of the stimulable phosphor sheet exposed to the radiation. Also, the filter, which has transmitting properties with respect to the erasing light and has good absorbing properties with respect to the radiation, is located on the side of the erasing light source, which side stands facing the stimulable phosphor sheet. Therefore, back scattering of the radiation is capable of being prevented from occurring. Also, the size of the radiation image recording and read-out apparatus as a whole is capable of being kept smaller than the cases where a lead plate for absorbing the radiation is provided. Further, the structure of the radiation image recording and read-out apparatus is capable of being kept simpler than the cases where the lead plate for absorbing the radiation is provided.
With the radiation image recording and read-out method and apparatus, wherein the filter is a filter, which transmits only light constituted of light components having wavelengths longer than wavelengths of the ultraviolet region, the problems are capable of being prevented from occurring in that new trapped electrons are formed on the stimulable phosphor sheet, i.e. new energy is stored on the stimulable phosphor sheet, due to light components of the erasing light, which light components have wavelengths shorter than the wavelengths of the ultraviolet region. Therefore, the erasing efficiency is capable of being enhanced.
With the radiation image recording and read-out method and apparatus in accordance with the present invention, the stimulable phosphor sheet may be kept stationary at the position for image recording, and the image read-out operation may be performed with the image read-out means comprising (a) the read-out unit for irradiating the stimulating rays to the stimulable phosphor sheet in the one-dimensional direction along the main scanning direction and detecting the light, which is emitted by the stimulable phosphor sheet when the stimulating rays are irradiated to the stimulable phosphor sheet in the one-dimensional direction, and (b) the unit moving means for moving the read-out unit in the sub-scanning direction. In such cases, a space for the conveyance of the stimulable phosphor sheet and conveyance means are not necessary. Therefore, the size of the radiation image recording and read-out apparatus as a whole is capable of being minimized.
Further, the read-out unit may comprise the linear stimulating ray source, which linearly irradiates the stimulating rays to the area of the stimulable phosphor sheet, and the line sensor, which is located along the linear area of the stimulable phosphor sheet exposed to the linear stimulating rays and photoelectrically detects the light emitted by the stimulable phosphor sheet when the stimulating rays are irradiated to the stimulable phosphor sheet. The linear stimulating ray source is capable of being formed to a size smaller than a point scanning type of light source, with which one light beam is deflected and caused to scan on the stimulable phosphor sheet. Also, the line sensor is smaller than a photomultiplier, or the like. Therefore, in such cases, the size of the read-out unit as a whole is capable of being set to be small, and the size of the radiation image recording and read-out apparatus as a whole is consequently capable of being set to be small.